I catch my first glimpse of Libby Purves through the window of 'Jericho' - the Jericho Caf in Oxford......

• Shadow Child by Libby Purves is published in hardback by Hodder & Stoughton,price £17.99

I catch my first glimpse of Libby Purves through the window of 'Jericho' - the Jericho Caf in Oxford. Outside, students with rucksacks are speeding past on bicycles, late for mind-expanding lectures; slow-moving delivery vans are negotiating tight corners; bearded, suited, coiffed, bright, dowdy, multifarious characters are shopping, chatting, rushing, dawdling along the pavements.

But there, with her coffee, she sits, frozen for a moment in time.

For a fleeting second, it calls to mind a scene in her latest novel. Against the background of a funeral, there's a window - a stained-glass window - where saints, immortalized in their sacred colours, are framed in static eternity; but behind the glass, in the churchyard outside, is juxtaposed the moving outline of a tree, tossing wildly its branches in the wind.

(Time and tide wait for no man, says the pragmatic proverb. "Stop all the clocks", said Auden.)

And time moves on.

She probably knows that interviewing journalists is not the easiest of tasks. But meeting Libby Purves is like being invited into a roomful of friends. Funny, friendly, easy. "I'm always in and out of this caf," she says, guiltily hiding a sugary croissant from the photographer's dispassionately-curious lens. "Bill Nighy says that the best thing about 'making it' is being able to go out for breakfast every morning!"

We instantly find things in common: we've both interviewed Tony Benn. "Once politicians live beyond 75, they become national treasures," she comments, wryly. "One day, they'll be affectionately saying, 'Oh that John Prescott!'".

It's partly the humour that puts you at your ease; but it's also the distinctive wavelength of the familiar voice that flows over the airways 'Midweek' on Radio 4. Soothing - yet as far from soporific as spice from sugar; the kind they should put on emergency announcements (except for the danger that you'd delay action in favour of settling back and listening to more).

I'm here to talk to her about her latest novel, Shadow Child; a novel it's difficult to describe without mis-selling. Because it is a light and funny read; a beautifully-written tale of grief, love, relationships and (sometimes) kooky middle-class values. Yet while the words seem to skim the surface like a flat stone bouncing over waves, you emerge to realise you've been on a far more profound journey; a journey to the bottom of the sea, fathom deep in emotion.

It's about Marion and Tom, who've lost their only child, Sam, in a randomly-stupid accident, bereft of dignity or meaning, on the eve of his 21st birthday. It's about the effect of his death on their relationship; and it's about a fierce woman who turns up unexpectedly, angrily demanding to see their dead son - a strange woman: an untidy, political, I-hate-men, city-streets sort-of-woman whom they'd never, in their rural idyll, have expected to cross their neat path. Why is she there? What does she want? And what connection could she possibly have with their beloved, deeply-missed child?

Clearly, Shadow Child is not autobiographical. But also clearly, there are parallels that need to be explored. Libby Purves and her husband, the writer and broadcaster Paul Heiney, lost their elder child, Nicholas at the age of 23. His was no random death: he took his own life after a bravely-fought battle with mental illness. Yet both boys - the fictional and the real - leave legacies. If I were to tell you Sam's, I'd be giving away the plot. But in Nicholas's case, that legacy was 35,000 words, scrawled on scraps of paper, diaries and Post-it notes, stuffed away in his room and discovered after his death nearly three years ago. Words, now published, that have inspired thousands with their wisdom, their uncanny maturity, and their sheer beauty.

Although Libby has spoken openly and often about Nicholas, the questions on my notepad that refer to him are lightly pencilled. In fact, she turns to the subject naturally and immediately. "After our son died nearly three years ago," she says, "I started two other novels, just to see if I could still write fiction; but they both fizzled out. It was as if there was another book wishing to be written that was closer to home.

"I certainly didn't want to write about Nicholas; I didn't want to write about me and my grief though, God knows, enough people asked me to. Shadow Child is not autobiographical - it's fiction. But I had had so many letters from people all over the country, and sometimes from other parts of the world, describing their own their feelings and their experiences; and I had learned so much about the processes of recovery, and the weirdness of grieving - particularly for a lost child - that I found myself writing the first chapter."

The letters she mentions provided other themes, too: the desperate human need to see family genes continue; the joy - status even - that grandchildren bring. Grandchildren that those who have lost an only child - like Marion - will never know.

And then there's the stained glass window; the idea that, even when the world as you know it has ended, branches carry on thrashing; clocks keep on ticking.

"You become terribly aware, after any death, of the extraordinary chaotic persistence of life. It goes on and you can't stop it. Life is always fighting to get back in and batter you around; you might as well swim in it because the tide doesn't really carry you away from the person you've lost; but you fear it will. I got so many letters from people - especially men - saying: My wife has never been out since; my wife has never worked again. Part of you wants to shake them. And part of you wants to understand and say: Yes, I can see that. But you can sort of choose."

And Libby has chosen. She, Paul and their daughter, Rose - also a novelist - chose to publish Nicholas's writings as The Silence at the Song's End, with the help of Duncan Wu, his Oxford tutor. Rose was determined it would not be sold overtly in aid of charity: she wanted the book to be bought purely because of the quality of writing. As indeed it has. (It seems no coincidence that its natural place on the bookshop shelf lies between Seamus Heaney and George Herbert.) Instead, the profits go quietly towards helping individual causes.

Libby has also chosen to continue with her career. It's a measured choice: "For his honour, I was not going to give anybody the chance to say: Oh what that boy did wrecked that family; she's never worked again".

It's a career that began here in Oxford, with a first-class honours degree in English, followed by a stint as a reporter on BBC Radio Oxford. "I couldn't drive so I had a moped with 'L' plates, and that's how I got to interesting places like Burford. It had a dynamo light, so if I was lost at night and wanted to read signposts, I had to lift up the front wheel and go vrrmm, vrrmm to keep it bright enough to see the road signs!

"And Witney... There's something about Witney I adore. I've never forgotten sitting next to Richard Early [of Early's Blankets] at the loom, when he just started quietly singing The Foggy, Foggy Dew: 'I live by myself/ And I work at the weaver's trade...'. He'd kind of forgotten I was there. It was one of those moments with the tape recorder when I was praying to God that it was working: a real moment of dreaming about the weaver's trade and being proud of the blankets. Even today, I get a lump in my throat when I see a blanket with Witney in the corner."

Sad, I agree.

"Ah, but," she laughs suddenly, "duvets are much easier."

You'd think she'd be proud of being the first woman, and youngest ever (at 28), presenter on Radio 4's flagship Today programme - and, of course, she is; but her real sense of achievement comes through the fact that she worked her way up through the technical ranks. "Sue MacGregor says there was an awful lot of sexism; I just never noticed. I had three brothers and, if I didn't agree with them, I slapped them about a bit. I never felt dumbed down by being female."

What about interviewees?

"The point is that John [Timpson] and Brian [Redhead] were both a lot older than me, and a lot more experienced. Therefore, if the Prime Minister was coming in, they would tend to do those interviews. John used to say, 'Your problem, young lady, is that you peaked 20 years too early'. Which was nice. On the other hand, I got the big trip to Beijing. I got the European Summits."

Any horror moments?

"Endless. But you're not doing open heart surgery. No one's going to drown just because you made a tit of yourself on the radio."

Ask her for a list of favourite interviewees, and she'll tell you it's the people you've never heard about who delight and surprise her. Indeed, Libby has a reputation for helping shy people to shine on air.

"Everyone has their story, whatever it is. Sometimes the stars are more difficult to get at though, occasionally, one really surprises you. It happened with David Attenborough the other week. I happened to ask: 'Does wildlife make you happy?' And he absolutely paused in his tracks. So I asked if it was consoling, and he said, 'Yes'. And we both came together around the fact that there are consolations in all sorts of moments, such as seeing a skein of geese flying; they'd be flying if you weren't there; and when you're gone, there'll be more geese flying."

She's also a columnist, writing in The Times each week. Her thoughts are well-researched, rarely aimed personally - and she never is afraid to say she's changed her mind.

"I was turned around about poor old Jade Goody. I thought she should not have been exposed in her last days but, in the end, I think she has done some good. Though, frankly, everyone who's reading that stuff should get a life. If you want to be kind to a cancer sufferer, find one down your own street."

Does she feel exposed, sometimes, putting her opinions out there?

"Oh God, yes. Everything published in a newspaper now goes online and attracts a tail of anonymous bitchery. We [the columnists] have to stand up and be counted; then a lot of vicious people put stuff underneath. I think they should have to put their names and where they live - I hate the anonymity. But then, of course, you find some comments that are wise and wonderful."

She's not, she says, 'the blessed Peter Tatchell', but she is well known for speaking out on gay rights. Earlier this year, to mark Lesbian, Gay, Bisexual, and Transgender/transsexual (LGBT) Awareness Week, she spoke for the motion 'This House Would Rather Be Gay' at the Cambridge Union Society against Stephen Green of Christian Voice.

"It's all about love," she says, simply. "There's a lovely title to Simon Callow's book about his bizarre friendship with the old lady, Peggy Ramsay; it just says 'Love is where it falls'. The Civil Partnership Act was the one thing for which I can almost forgive New Labour all the bad things. The great Jan Morris is one of my heroes. She was born transsexual; 50 years after her first marriage, she has contracted a civil partnership with Elizabeth, the former wife, and they have lived together ever since. How's that for life-long love? How many straight couples have done that well?"

It is, I suggest, reminiscent of an Elizabeth Barrett Browning poem. Instead, she quotes Shakespeare:

Love is not loveWhich alters when it alteration finds,Or bends with the remover to remove.

"I've had gay characters wandering in and out of my novels quite happily, and I always try to make it normal."

Shadow Child is her 12th novel. She's also the author of 13 non-fiction books, several of which detail her passion for sailing. Being at sea, she says, is a good way of putting life into perspective.

"Nicholas was like that, too. Nicholas found at sea a kind of resolution that he never really found anywhere else. It's very much in his book, in his sea logs: he calls the Pacific 'the least lonely nowhere in the world'."

It's another facet they share, along with their lyricism, their understanding, their tolerance, their appreciation of the world. The stone-carver John das Gupta, who created a memorial stone for Nicholas, asked if he could use some of his words for a piece for the Memorials by Artists permanent exhibition at West Dean in West Sussex. The words he chose are from Nicholas's book; an exquisite phrase about the diversity of life that leaps off the page and embeds itself in the reader's mind forever: "Remember how the streets ring out for every soul that thought and felt and walked through them in weakness and in strength".

"When I first saw those words, I thought they were a quote: Is this Middlemarch, I wondered?"Libby Purves says. "Then I found early versions of it and I thought: That's all him; he is extraordinary. At 23, Nicholas had got further in his thinking than a lot of people do when they're 55. He was extraordinarily gentle and humane all his life."

Time stands still, time freezes, time moves on. But some things remain.

Extraordinary boy; extraordinary mother; extraordinary family.

Libby Purves OBE will be at Calcot Manor, near Tetbury, to talk about Shadow Child on Monday, May 11. Tickets cost 25 for a two-course lunch and wine. More details from 01666 890391, www.calcotmanor.co.uk

Shadow Child by Libby Purves is published in hardback by Hodder & Stoughton,price 17.99

For more on Nicholas Heiney and his writing, visit www.songsend.co.uk

You currently have JavaScript disabled, functionality will be limited

Actress and Writer Libby Purves

• Shadow Child by Libby Purves is published in hardback by Hodder & Stoughton,price £17.99

The Cotswolds’ very own Prince of Wales turns 70 this month, so we looked back on some of the highlights of his life and career, and wondered what birthday pressies we would buy for the man who has the world at his feet

Radio DJ Paul Gambaccini has secured a payout from prosecutors over unfounded allegations of historical sex offences. The presenter, 69, was arrested in 2013 over a claim he sexually assaulted two teenage boys in the early 1980s. Mr Gambaccini always denied the claims, calling the case “completely fictitious”. He spent a year on bail before the case was dropped. Two years later he gave this interview to Katie Jarvis

The environmental charity set up to protect Stroud’s industrial heritage now enhances the lives of its own volunteers. Katie Jarvis meets chief executive Clare Mahdiyone to hear about her Cotswold Life

Alex Caccia was in two minds about setting up Animal Dynamics as a limited company, but a shark attack warning changed all of that. Tanya Gledhill meets a man on a mission to change propulsion, one animal at a time

When Charles Martell became the latest High Sheriff of Gloucestershire, he started discovering things about the county he never knew – not to mention things about himself, too. Katie Jarvis spoke to him about saw pits, walnuts, peaceable towns and pink-headed ducks